The Grotthuss mechanism, proposed in 1806, describes the transport of protons in aqueous solution and other hydroxylated solvents. In the Grotthuss mechanism, protons are transferred between water molecules through a series of hydrogen bond rearrangements. This process can be represented as:
H3O+ + H2O → H2O + H3O+
In this reaction, the proton (H+) is transferred from the hydronium ion (H3O+) to a water molecule. The water molecule then becomes a new hydronium ion, and the process can continue.
The Grotthuss mechanism is a cooperative process, meaning that the proton transfer is facilitated by the surrounding water molecules. This is because the water molecules are hydrogen-bonded to each other, and these hydrogen bonds can be rearranged to allow protons to move through the solution.
The Grotthuss mechanism is a very efficient way to transport protons in water. It is estimated that protons can travel through water at a speed of up to 10^7 cm/s.
Eigen mechanism
The Eigen mechanism, proposed in 1964, is a different mechanism for proton transport in water. In the Eigen mechanism, protons are transferred between water molecules through a series of proton-jump reactions. This process can be represented as:
H3O+ + H2O → OH- + H2O + H+
In this reaction, the proton (H+) is transferred from the hydronium ion (H3O+) to a water molecule, resulting in the formation of a hydroxide ion (OH-) and a water molecule. The proton can then jump to another water molecule, and the process can continue.
The Eigen mechanism is a non-cooperative process, meaning that the proton transfer does not require the participation of surrounding water molecules. This is because the proton-jump reactions can occur between any two water molecules that are close enough together.
The Eigen mechanism is not as efficient as the Grotthuss mechanism for transporting protons in water. It is estimated that protons can travel through water at a speed of up to 10^5 cm/s.
In summary, the Grotthuss mechanism and the Eigen mechanism are the two main mechanisms for proton transport in water. The Grotthuss mechanism is more efficient, but the Eigen mechanism can occur in more confined environments.
